Compound piston for internal-combustion engines



Feb. 6, 1923.

P. J- MILLER.

COMPOUND PISTON FOR INTERNAL COMBUSTION ENGINES.

' FILED JULY 15. @921.

the relative' axial' Patented Feb. e, 1923.

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PAUL J. MILLER, OF BIRMINGHAM, ALABAMA.

Application filed'July 15, 1921.

To all whom it may concern:

Be it known that 1 PAUL citizen of the United States of America, residing at Birmingham, in the county of Jefferson and State of Alabama, have invented certain new and useful Improvements in'Compound Pistons for Internal- Combustion Engines, of which the followingdis a specification.

l y-invention relates to a compound p1ston for internal combustion engines, the elements of the piston in their relative movements being controlled by air cushions which are automatically obtained and which are subject to regulation in order to control play between the elements J. MILLER, a

of the piston.

It is characteristic of my invention that the innerpiston shall carry the wrist pin and that the outer piston shall be free to rotate about and to move axially of the inner piston. v One advantage of this construction is derived from the freedom of the outer piston to turn about the inner piston and thus pre vent uneven wear of, and a tendency to score, the cylinder walls.

My invention contemplates controlling the relative axial movement between the pistons by air cushions which are automatically produced and maintained and one at least of which iscontrollable so as to limit the free play between the pistons. The importance of the axial play and of the cushioning control thereof are manifold. It will gradually relieve excessive jars and strains delivered to the crank shaft from explosions occurring on or near dead center positions of the pistons; the air cushions will serve to prevent actual contact between the pistons and-thus relieve the crank shaft of mechanical jars; the excessive initial thrust imparted by the explosion to the outer piston while near dead center position will be in part absorbed by an air cushion and later applied, at a more efi'ective leverage angle to the crank; the inner piston having a limited play in both directions from dead center position before moving the outer piston will cause a reduction in the dead center load on the cranks and will reduce the vibration and cause the engine to run more smoothly; and, finally, as the outer piston will ride higher on its air cushion during its scavenging stroke than on its coni- Serial N 0.

pression stroke it will more effectively scavenge the cylinder.

These and otheradvantages of my invention will be better understood by reference to the illustrative embodiment of my inventlon which is shown in detail in the accompanying drawings, in which Fig. 1 is a sectional tons of a compound wardly under after the upp View showing the pispiston moving clownthe. initial power stroke just or air cushion has absorbed the initial thrustfi Fig. 2 shows the compound piston in partial cross section moving upwardly on a scavenging stroke.

Fig. 8 is a detail view piston illustrating clearly.

of part of the outer the screw r ng more Fig. 4c is a half sectional view of the inner piston.

Similar refe ilar 1 designates gine cylinder, which is conne IQDCQ numerals refer to simparts throughout the drawings.

a conventional explosive enthe crank (not shown) of owed to a wrist pin 3 mounted in the inside piston t. This piston has the outer surface form an air c and the inner Throu h the i ton i of its inner end reduced to ushion chamber 5 between it wall of the outside pistonG. nner reduced end of the pisf provide a series of air relief ports 7 lying in a horizontal plane above a packing ing 8 and substantially spaced from the upper end of the chamber 5, above which is a packing ring 9 which engages the inner cylindrical surface of the piston 6. 'The upper end of the inside piston 4 carries any desired 12, against which The sleeve can be A sleeve 11 number of additional packing rings 10 so as'to effectively pack the joint between outside pistons so as to make as possible without interferrelative axial movements of is screwed into the reduced lower end the packing ring 8 works. screwed into and out of above its the plston to regulate the depth of the annular air cushion the piston i is seat formed in a bushing 13 ceives a taper The head of a taper valve which seat revalve let having a stem 15 chamber 5. provided with which projects down into the chamber in the piston i and carries a seat 16 for the coil spring 17., for the stem which surrounds a guide 19 and at its upper end bears against the perforated base of: the bushing. The valve as thus disposed will seat against pressure between the heads of the two pisby the sleeve 11 and when this occurs a body o f airwill be trapped in the annular chamber 5 forming the lower air cushion which is the medium by which the inner piston draws down with it the outer piston. As the piston heads tend to move apart no appreciable vacuum will occur to retard the relative downward movement of the inner piston be- 7 cause the valve 14: will open when necessary to prevent a vacuum. At the completion out the stroke and while holding its lower dead center position the only weight and load bearing on the crank shaft will be that of the inner piston as the outer piston will be floating between the air cushion 5 and the air cushion between the piston heads. On the compression stroke, the inner piston moves relatively to the outer piston a suflicient distance to compress the air cushion between the piston heads, causing the latter to lift the outer piston with it. The inner piston 4L thus gradually takes on the load oi the outer piston and there is no jar or shock to the engine. At the completion of the compression stroke the air cushion between the piston heads will be compressed to an equal extent with the charge in the cylinder. Upon firing, the explosion will take effect on the outer piston first further compressing the air cushion between the piston heads approximately equal the the compound piston. This compression of the air cushion between pistons commences with the crank nearly on dead centerand continues for a definite time interval during which the crank is moving farther from its dead center position and thus the heaviest shock of the explosion is not immediately and directlytransmitted to the crank sha-t't but the power thrust is imparted thereto in more or less gradual fashioi'i and over a much greater and more efiicient leverage sector of its angular travel than would be the case if a simple piston were used. Upon the completion of the power stroke the pistons will be approximately in the positions shown in Fig. 2 and as they move for the scavenging stroke the piston 4 will compress air in the chamber above it so as to lift with it the outer piston, but there being no pressure for the outer piston to work against it will ride much higher than during its compres the" sleeve in or outer gas pressure above sion stroke and to this extent will increase the displacement of the burnt gases and render a more efficient scavengingthan would be possible with a solid piston. By screwing the outer piston 6 the volumeo t the air trapped between the piston heads is controlled, because the sooner the ports 7 are closed the sooner the relative downward movement of piston a in the piston 5 is checked and hence the shallower the air cushion chamber between the pistons. By this meansl can regulate the compliession of the charge by regulatingjthe axial displacement between the pistons, it being understood that the inner'pistonhas always a fixed travel and" that the extent of the compression is entirely controlled by the movement of the outer piston. ,Itthus follows that the adjustable control ofthe relative axial movement-s between the pistons is vital to an exact control of the compression.

It is to be understood thatany valve mechanism maybe employed to function in the manner described forthe valve 14: to relieve a vacuum between the piston heads.

Having thus described my invention, what I claim as new and desire tosecure by Let ters Patent is y. v

1. In an explosive engine, a compound piston comprising an outer piston, an inner piston telescoped in the outer piston, a crank shaft connection carried by the inner piston, and means utilizing air cushions to control the relativeaxial play between said pistons. a

2. In an explosive engine, a cylinder and a compound piston working therein and comprising inner and outer pistons, a crank shaft connection to the inner piston, and adjustable means to trap air between the pistons on their down stroke. f

3. A mechanism in accordancewith claim 9,, in which the inner piston carries an upwardly opening valve means to relieve a vacuum between-the heads of the pistons on their down stroke. I

i. In an explosive engine, a cylinder and a compound piston therein comprising an inner piston having a crank shaft connection, an outer piston both rotatable and axially movable on the inner piston, automatic means to relieve the vacuum between the piston heads of the compound piston, and means responsive to air pressure to cushion the relative axial movements between the pistons. i x

5. In an explosive engine, a cylinder and a compound piston therein comprising an inner piston having a crank shaft connection, an outer piston both rotatable and axially movable on the inner'piston, and means to control the relative axial movements between the pistonsby trapped bodies of air.

6. In an explosive engine, a compound piston comprising an outer piston, an inner 1,444,423 piston working with piston rings in the outer piston, valve means to relieve a Vacuum between the piston heads, and oo-acting portions at the inner ends of the pistons to form an air trappin chamber, said chainher having relief ports adapted to be blanketed under predetermined conditions by the Witness:

outer piston. NoMIE WELSH.

7. A piston in accordance with claim 6, in which the portion of the outer piston which 10 blankets said relief ports is in the form of an axially adjustable sleeve.

In testimony whereof I afiix my signature.

PAUL J. MILLER. 

